This Photoelectric Detector is suitable to be used in security system in school, home yard, office building, etc.

How to Build an Infrared Detector:

Infrared detectors sound like very high tech equipment, but the principles behind them are quite simple. Though not particularly powerful, a self-made infrared detector can spot visitors at doors, register movement up and down stairways and alert you when pets go into areas where they are not allowed. Most of the components can be purchased at an electronics supply store for very little money and assembled using only a soldering gun and a little time.

Instructions

1. Tack the leads of a Sharp IS471 proximity sensor to a perfboard. You should place them within two or three holes of the edge to make the rest of the building process easier.

2. Bend an IR LED so that the emitter is at a right angle to the wiring and the cathode (short lead) is at the top.

3. Mount the LED to the perfboard directly underneath the proximity sensor, securing it in place with pins. That way, the perfboard will block the light from the LED and the proximity sensor will not detect it accidentally.

4. Slide the short lead (cathode) of the LED through the perfboard, two holes behind pin 3 of the proximity center. Then slide the long lead (anode) of the LED through the perfboard, two holes behind pin 2 of the proximity sensor.

5. Solder the cathode of the LED to pin 4 of the sensor and the anode of the LED to pin 1 of the sensor.

6. Solder the red (positive) wire of a 9-volt battery clip to pin 1 of the sensor (the solder will fuse it to both the pin and the anode of the LED).

7. Solder a short length of electrical wire to pin 2 of the sensor.

8. Place a 9-volt battery in the battery clip.

9. Connect the free end of the wire attached to pin 2 of the sensor to pin R3 of a 20-second record and play module.

10. Solder the black (ground) wire of the battery into the ground connection of the record and play module.

11. Cover the holes in the perfboard with black tape to keep unnecessary light from the emitter.

12. Place your hand in front of the emitter and move it closer slowly. When it gets closer than about a foot, the infrared detector will notice it and the record and play module will activate its sound. Set the emitter in the location you desire.

How Infrared Detector Work in Security Systems:

A. Infrared Detectors Use Infrared Light

In order to fully understand how infrared motion detectors work in security systems, users must first understand the function of infrared light. According to the National Aeronautics and Space Administration (NASA), infrared light exists in the electromagnetic light spectrum, and operates in a range of frequencies not visible to the human eye. The blanket term "infrared light" encompasses two frequency ranges, "near infrared," which operates at a frequency closer to that of visible light, and "far infrared," a range of frequencies closer to microwaves than to the visible spectrum. Because of the higher frequency range of far infrared, the infrared light possesses thermal properties that allow it to sense and detect very subtle temperature changes, and this temperature sensory ability is what helps detect movement in a home security system.

B. Infrared Detectors Monitor a Room

In a typical home or office security environment, infrared motion detectors mount on a wall or the ceiling. Once in place, the motion detectors use far infrared light beams to create a thermal image of the monitored area. Because every component in a home or office - including furniture, floors, walls and fabric - has a certain heat signature, the infrared motion detector quickly develops a "normal" image of the room and its fixtures. If this image changes, as it does when a person, animal or object enters the area under infrared monitoring, the detector′s built-in circuitry identifies the image change and sends a signal to the security system′s control panel.

C. Heat Can Affect Infrared Detectors

Due to the low cost and reliability of infrared detectors, according to Alarm System Reviews, the devices account for the majority of motion detectors in home security applications. Despite the reliability of the devices, though, they are far from infallible. Manufacturers of infrared detectors ship the devices with explicit mounting instructions that include strong warnings against placing the detectors near a heat source. Because the devices rely on thermal imaging, a heat source like a radiator or heat pump vent can quickly change the thermal appearance of a monitored area and trigger a false alarm. Likewise, an infrared detector mounted to face a window may sound an alarm when the sun sets or rises, or when other environmental factors cause a sudden change in ambient temperature.